This application incorporates by reference Taiwanese application Serial No. 89101714, Filed Feb. 1st, 2000.
1. Field of the Invention
The invention relates in general to a method and device of determining the slice level of a radio frequency ripple (RFRP) signal in an optical storage device, and more particularly to the method and device of using a radio frequency center (RFCT) signal, as the slice level of the RFRP signal when the optical storage device is on tracking.
2. Description of the Related Art
FIG. 1 is a block diagram illustrating the structure of an optical storage device. The optical storage device indicated here includes at least a CD-ROM drive and a Digital Versatile Disk (DVD) drive.
Referring to FIG. 1, a spindle motor 100 is used to drive an optical disk 101 to the required rotation speed. A sled motor 102 is used to drive the sled 105 which is equipped with an optical pickup head 104 for rough tracking and seeking operations. The tracking operation is used to drive the optical pickup head 104 to a certain track on the optical disk 101 for reading data.
Fine-tuning operations include focusing and tracking operations. The focusing operation involves the objective lens 120 running in a vertical direction in order to accurately read data on the optical disk 101 whereas the tracking operation involves the objective lens 120 running in a horizontal direction to find the desired track.
When a laser is focused on the optical disk 101, the reflected light is received by the optical sensor on the optical pickup head 104. Optical pickup head 104 outputs the signals corresponding to data stored in the optical disk 101 as well as signals for various servo controls.
The signals outputted from the optical pickup head 104 are transformed by a preamplifier 106 into radio frequency (RF) signals and other signals for various servo controls such as tracking error (TE) signal, RFRP signal, and RFCT signal. These signals are then inputted to the control integrated circuit (control IC) for processing. Included in the control IC 108 are, for example, a digital signal processor (DSP) in addition to other analog or digital circuitry. The control IC 108 obtains an output data by performing the demodulation and error correction of the received RF signals and sends out the output data to the decoder 112 and then the host computer 114 for further processing. Meanwhile, the control IC 108 processes the servo signals with necessary compensations and outputs to power amplifiers 116 and 118 to drive the spindle motor 100, the sled motor 102, the focusing actuator and the tracking actuator.
The microprocessor 122 is responsible for the overall operation of the disk as well as the user interfaces such as controlling the opening of the disk tray.
Generally, there is a phenomenon called run-out for the optical disk 101. The run-out phenomenon occurs due to the fact that the circular hole of the optical disk 101 is not located precisely in the center. As a result, when the optical disk 101 is spinning, the slight offset of the center hole causes track being read to run-out of the range of the objective lens 120. Moreover, vertical and horizontal vibrations sometimes occur when the optical disk 101 is spinning, and a misread of the track is caused. As can be seen, tracking is not a trivial pursuit and as a result, a tracking controller is needed. FIG. 2 is a block diagram illustrating the tracking servo apparatus of a optical storage device. Referring to FIG. 2, the tracking process is illustrated as follows. The optical sensor 200 receives the reflected light from the disk, and then outputs the received signals to the preamplifier 202. These signals are amplified by the preamplifier 202 and transmitted to the tracking controller 204 and then to the compensators 206 and 208 for the desired frequency response compensation of the system. The compensated signals are then amplified by the power amplifiers 210 and 212 to drive the objective lens actuator 214 and the sled motor 216, respectively. Then a position of the objective lens is obtained, and the position of the objective lens is fed back along with a disk eccentricity and vibration until the optical sensor 200 has exactly tracked the track needed.
In the above description, the tracking controller 204 and the compensators 206 and 208 mentioned are located in the control IC 108 mentioned in FIG. 1.
FIG. 3 illustrates various signals needed by the tracking controller 204 and the compensator 206 mentioned in FIG. 2. The signals inputted to the tracking controller 204 are transmitted from the preamplifier 202 mentioned in FIG. 2.
FIG. 4 is a timing diagram of various signals illustrated in FIG. 3. Before time T7, the objective lens moves outward relative to the optical disk whereas after time T7, the objective lens moves inward relative to the optical disk. During the outward movement of the objective lens (i.e. before time T7), there are negative and positive feedback periods. In the negative feedback period, for example, between time T1 and T3, the TE signal makes the objective lens move toward the track needed. On the other hand, in the positive feedback period, between time T3 and T5, the TE signal makes the objective lens move away from the track needed.
Referring to FIG. 4, when the objective lens is moving outward, the TE signal is in the negative feedback period when the slope of the TE signal is positive and in the positive feedback period when the slope of the TE signal is negative. On the contrary, when the objective lens is moving inward, the TE signal is in the positive feedback period when the slope of the TE signal is positive and in the negative feedback period when the slope of the TE signal is negative.
The TE signal is an index of the tracking operation. For example, during time T2 and T6, the amplitude of the TE signal is 0 which means that laser spot is on the track needed. However, when laser spot is located between two tracks, the amplitude of the TE signal is also 0. An example is time T4 in which TE is zero during the positive feedback period. On the other hand, when laser spot is on the edge of a track, the amplitude of the TE signal is highest. For example, at time T1 or T3.
The RFRP signal is derived from the RF signal which is the data signal read from the optical disk. When the laser spot is tracking on the desired track, the amplitude of the RF signal is highest; when the laser spot is between two tracks, the amplitude of the RF signal is lowest. The RFRP signal is obtained either by a difference value between the bottom envelope and the peak envelope of the RF signal or by a low-pass filtering of the RF signal.
When the laser spot is tracking on the track 103 in FIG. 1, the amplitude of the RFRP signal is highest while when the laser spot is between two tracks, the amplitude of the RFRP signal is lowest.
The relationship between the phases of the RFRP signal and the TE signal is illustrated as follows. When the objective lens is moving outward, that is, before time T7, the phase of the RFRP signal is ahead of the phase of the TE signal by 90 degrees. On the other hand, when the objective lens is moving inward, that is, after time T7, the phase of the RFRP signal is behind the phase of the TE signal by 90 degrees as shown in FIG. 4.
In FIG. 4, a radio frequency zero crossing (RFZC) signal is derived from the RFRP signal. While tracking in the conventional technique, there is a fixed reference value, for example the DC level of the RFRP signal during tracking off period, for the slice level of the RFRP signal. When the RFRP signal is larger than the slice level, the RFZC signal is at high level while the RFRP signal is lower than the slice level, the RFZC signal is at low level. Moreover, the RFZC signal is the same as the positive or negative feedback periods of the TE signal. That is, when the RFZC signal is at high level, the TE signal is in negative feedback period and as a result, the TE signal can be utilized for tracking. On the contrary, when the RFZC signal is at low level, the TE signal is in positive feedback period which results in the tracking servo apparatus to move in the opposite direction of the track needed and so during the positive feedback period, the TE signal cannot be used for tracking.
Owing to the characteristics of the RFZC signal mention above, the RFZC signal is used as an index for whether TE signal is inputted to compensator 206 as the TE_input signal.
During the positive feedback period, the TE signal causes the tracking servo apparatus to move in the wrong direction and so the TE signal in the positive feedback period is not adopted as the TE_input signal. The TE_input signal is maintained in the peak amplitude of the TE signal. The so-called hysteresis effect can prevent errors due to the tracking servo apparatus as well as reduce the time needed for tracking operation.
Nevertheless, the conventional method of using a fixed reference value as the slice level of the RFRP signal can produce problems under some conditions. For example, during the tracking operation, sometimes there are disturbances resulting in the waveform of the RFRP signal to flutter up and down, that is, the dc value of the RFRP signal is not horizontal but fluctuates up and down. This situation occurs when the tracking operation is at high speed, the reflection rate decreases, or due to a defect of the CD-ROM disk. The situation is especially serious for the DVD ROM disk.
As such, if the slice level of the RFZC signal is a fixed reference value, the RFZC signal obtained is erroneous as well as the determination for the positive or negative feedback periods. This results in unstable tracking operation. If the fluttering degree of the RFRP signal is too high, the RFRP signal does not intersect the slice level, causing errors to occur and leading to the failure of the tracking operation. Ultimately, data on the CD-ROM disk cannot be read correctly.
It is therefore an object of the invention to provide an improved and simplified method and device for determining the slice level of the RFRP signal when tracking which effectively solves the problem mentioned above and achieves the purpose of the tracking operation.
The invention achieves the above-identified objects by providing a method of determining the slice level of a RFRP signal for the purpose of the tracking operation in a tracking controller of an optical storage device. The optical storage device receives a TE signal an RFCT signal, and the RFRP signal and then outputs a TE_input signal related to the slice level. The method includes the following steps: a. obtaining a count value when the absolute value of the TE signal is smaller than a threshold value; otherwise, resetting the count value; b. otherwise, outputting the TE signal as the TE_input signal unless the count value is smaller than a predetermined count value; and c. if the count value is smaller than a predetermined count value, outputting the TE signal as the TE_input signal when the RFRP signal is greater than the RFCT signal and otherwise outputting a peak value of the TE signal as the TE_in put signal.
The invention achieves the above-identified objects by providing a control circuit using a RFCT signal as the slice level in an optical storage device, outputting a TE_input signal according to a TE signal, RFCT signal, and RFRP signal. The optical storage device includes a first comparator, counter, second comparator, and third comparator. The first comparator is for comparing the TE signal with a threshold value. The counter generates a count value when the amplitude of the TE signal is smaller than the threshold value, and resets the count value when the amplitude of the TE signal is larger than the threshold value. The second comparator outputs the TE signal as the TE_input signal if the count value is greater than a predetermined count value. The third comparator is activated when the amplitude of the TE signal is larger than the threshold value or the count value is smaller than the predetermined count value. In addition, the third comparator outputs the TE signal as the TE_input signal if the RFRP signal is larger than the RFCT signal; otherwise, the third comparator outputs the peak of the TE signal as the TE_input signal.